1. Field of the Invention
The present invention relates to a substrate spin cleaning method and apparatus for cleaning semiconductor wafers, glass substrates for photomasks, glass substrates for liquid crystal displays, substrates for optical disks and the like, in which a cleaning liquid such as deionized water is supplied to a surface of a substrate spun about a vertical axis. The invention relates also to a method of measuring a pressure of a cleaning device in such a substrate spin cleaning apparatus.
2. Description of the Related Art
Conventional substrate spin cleaning apparatus are disclosed in Japanese Utility Model Publication (Unexamined) No. 1-107129 and Japanese Patent Publication (Unexamined) No. 3-52228, for example. In these conventional apparatus, a cleaning liquid is supplied to the surface of a substrate spun about a vertical axis, and a cleaning device (e.g. a cleaning or scrubbing brush) is moved over the substrate surface. The cleaning device contacts the substrate under a predetermined pressure to remove particles and impurities from the substrate surface. The particles and impurities removed are caused to flow with the cleaning liquid outwardly from the substrate by the centrifugal force due to the spin of the substrate.
To displace the cleaning device horizontally over the substrate surface, an arm having the cleaning device is rigidly attached to a support shaft rotatable about a vertical axis. A motor or the like is operatively connected to the support shaft to rotate the support shaft, thereby to displace the cleaning device horizontally over the substrate surface.
The support shaft is vertically movable to move the cleaning device, in combination with the rotation of the support shaft, between a position for cleaning the substrate and a position upward therefrom and between a cleaning position on the substrate and a retracted position displaced from the substrate. Further, the vertical movement of the support shaft is utilized to set the cleaning device relative to the substrate. In this instance, the operator checks to ensure an appropriate contact between the substrate and the cleaning device by adjusting an amount of the depression of the cleaning device upon the substrate according to the type of layer formed on the substrate (e.g. aluminum, oxide, nitride, polysilicon, patterned or bare silicon layer) and the property or type of contaminant adhering to the substrate.
In the conventional apparatus, the cleaning device in the cleaning position is at a fixed height. The pressure applied from the cleaning device to the substrate is determined once and for all, based on the height of the cleaning device fixed by an initial setting.
Conventionally, the pressure applied to the substrate is adjusted by varying an amount of depression of the cleaning device upon the substrate. It has been difficult for different operators effecting this adjustment to set a constant amount of depression upon the substrate at all times. This causes such inconveniences that a slight difference in the setting results in a difference in cleaning performance and that the substrate surface could be damaged. Further, a difference may occur between the predetermined height of the cleaning device and the expected pressure applied to the substrate, which may depend on the type of cleaning device used, or may be due to variations arising from using attachment of the cleaning device or may be relative to the position between the cleaning device and a substrate supporting device. Such a difference also lowers cleaning performance.